1. Field of the Invention
The present invention relates generally to a front drive electrical scooter, and in particular to a device for compensating directional offset caused by yawing of front wheel of the electrical scooter.
2. The Related Art
The improvement of technology and medical care extends life of human beings. The old and the disabled are best benefited from the modern technology and medical care. A lot of different supportive devices have been developed for helping the old and the disabled to transport themselves in an extended area so as to improve their living standard without particular care by other supporting medical personnel. Wheelchairs have been one of the most commonly known supportive devices for the old and the disabled to transport themselves in short distances. However, for those very weak or those having hand or arm injured, they still need other people""s help in moving the wheelchairs.
Electrical wheelchairs or electrical scooters that are equipped with electrical motors allow a person to move oneself without great effort and thus are particularly suitable for those whose arms are weak or injured. The electrically powered wheelchairs and scooters are also advantageous as compared with vehicles equipped with engines powered by fossil fuels for environmental protection.
The electrical scooters can be either front drive or rear drive. In a rear drive electrical scooter, there are two rear wheels mounted to a chassis and one or more electrical motors are mechanically coupled the rear wheels for driving the chassis. The rear drive electrical scooter also has a front wheel mounted to the chassis and a steering shaft rotatably mounted to the chassis and extending from the chassis in substantially a vertical direction. The steering shaft is fixed to the front wheel for swiveling the front wheel to control the moving direction of the electrical scooter.
The rear drive electrical scooter comprises a chassis to which two rear wheels and one front wheel are mounted. An electrical motor is mounted to the front wheel for driving the front wheel. Similarly, a steering shaft is mounted, in an upright manner, to the chassis of the electrical scooter for swiveling the front wheel to change and control the moving direction of the electrical scooter. The motor is mounted to one side of the front wheel and may thus exert a torque to the front wheel and thus the steering shaft due to unbalance of weight caused by the motor. The unbalance of weight or the torque causes the front wheel to consistently yaw or swivel to one side, leading to directional offset of the electrical scooter during the movement of the electrical scooter and thus being unsafe to the scooter rider. The rider of the electrical scooter must apply a force on the steering shaft to counteract the yawing caused by the weight of the motor and compensate the directional offset. In addition, directional offset of the scooter may damage the parts thereof by wearing parts out in a short period and thus shortening the service life thereof.
FIGS. 9-11 of the attached drawings show a conventional front drive electrical scooter, which is broadly designated with reference numeral 100 throughout the drawings. The electrical scooter 100 comprises a chassis 102 having front and rear ends (not labeled) to which a front wheel 104 and two rear wheels 106 are respectively and rotatably mounted. A seat 108 is mounted on the chassis 102 in the proximity of the rear end of the chassis 102. A steering shaft 110 is mounted to the front end of the chassis 102 in a substantially upright manner. The steering shaft 110 has an upper end to which a control device 112 is mounted. Two handles 114 are mounted to the steering shaft 110 and extend in opposite directions from opposite sides of the steering shaft 110.
The electrical scooter 100 further comprises an electrical motor 116 that is controlled by the control device 112. The motor 116 is mounted to one side of the front wheel 104 and is mechanically coupled to the front wheel 104 for driving the front wheel 104. In the conventional electrical scooter 100 shown in the drawings, the motor 116 is located on the right side of the front wheel 104. However, it is obvious to those having ordinary skills in the art the arrange the motor 116 on the left side of the front wheel 104, as illustrated in FIG. 12A of the attached drawings, or to have the motor 116 partially above the front wheel 104 as illustrated in FIG. 12B.
To make the front wheel 104 move in the straightforward direction, the front wheel 104 is angularly offset from the steering shaft 110 by an angle X in the frontward direction, as best seen in FIG. 11. Due to the angle, the weight of the motor 116 that is mounted to the right side of the front wheel 104 induces a torque on the steering shaft 110, causing the front wheel 104 to yaw rightward as shown in FIG. 10 that in turn leads to directional offset of the scooter in the moving of the scooter. As mentioned above, the directional offset makes the electrical scooter 100 to consistently move rightward unless the yawing is compensated by a counterforce applied to the steering shaft 110 by the rider. Such directional offset also causes wearing and other undesired damage to the parts of the electrical scooter 100, shortening the service life thereof.
It is thus desired to provide an offset compensating device for electrical scooter to overcome the above problems.
Accordingly, an object of the present invention is to provide a device for maintaining the front wheel of a front drive electrical scooter in a straightforward direction by eliminating directional offset caused by weight unbalance.
Another object of the present invention is to provide a device for eliminating yawing of front wheel of a front drive electrical scooter in order to extend service life thereof.
A further object of the present invention is to provide a front drive electrical scooter having enhanced operation safety.
To achieve the above objects, in accordance with the present invention, there is provided an electrical scooter comprising a chassis having front and rear ends to which front and rear wheels are mounted. A seat is mounted on the chassis for supporting a rider thereon. A steering shaft is rotatably mounted to the front end of the chassis in an upright manner and has a lower end attached to the front wheel for swiveling the front wheel. A control device is mounted to an upper end of the steering shaft. An electrical motor is mounted to one side of the front wheel and coupled to the front wheel for driving the front wheel under the control of the control device. Since the motor is mounted to one side of the front wheel, the weight of the motor induces a torque to the steering shaft and thus yawing the front wheel and making directional offset of the scooter in the moving thereof. An offset compensating device is provided to overcome the directional offset of the electrical scooter. The offset compensating device comprises a resilient element, such as a leaf spring, a torsional spring or a helical spring, arranged between the steering shaft and the chassis to apply a force to the front wheel for counteracting the weight of the motor thereby compensating the directional offset and maintaining the front wheel in a straightforward direction.